1. Field of the Invention
The present invention relates to apparatus for nondestructive inspection and testing of articles, and more particularly it relates to apparatus for acoustic-emission inspection of articles.
2. Description of the Related Art
There is widely known an apparatus for acoustic-emission determination of the coordinates of a developing crack in an article, comprising a plurality of channels each including a serial connection of a transducer of acoustic emission signals, positionable on an article, under inspection, and an amplifier of signals of acoustic emission. The outputs of the amplifiers of acoustic emission signals of all channels are connected to the first inputs of an encoder. Connected to the first outputs of the encoder are the first inputs of respective shift registers in a number equalling the number of the channels. The outputs of all shift registers are connected to the inputs of the first OR gate and to the first input of an electronic computing unit having its output connected to the input of a registration unit. The output of the first OR gate is connected to the respective first inputs of the first and second flip-flops. The first output of the first flip-flop is connected to the second input of the encoder. The second output of the first flip-flop is connected to the first input of a counter. The apparatus further comprises a second OR gate of which the first input is connected to the second output of the electronic computing unit, the second input is connected to the first output of the counter, and the output is connected to the second inputs of the respective shift registers, to the second input of the first flip-flop, and to the first input of the third OR gate. The second input of the third OR gate is connected to the third output of the electronic computing unit. The output of the third OR gate is connected to the second input of the second flip-flop.
The apparatus also comprises a series connection of a clock pulse generator and an AND gate, the second input of the electronic computing unit being connected to the output of the second flip-flop, as is the second input of the AND gate, and the third input of the electronic computing unit being connected to the digit outputs of the counter. The third inputs of the shift registers are connected along with the second input of the counter, to the output of the AND gate.
When a developing crack evolves in the article, a signal comes to the transducer of acoustic emission signals, and the code of the channel which has been the first to receive the acoustic emission signal is written in the lower-order digits of the shift registers. Then this code is shifted in the shift registers through the number of digit positions corresponding to the time interval passing before the instant of reception of an acoustic emission signal by another channel, whose code is written in the lower-order digits of the shift registers.
The appearance of the code of the first-mentioned channel at the output of the registers triggers the process of data transfer to the electronic computing unit. The counter counts the number of the digit positions between successive codes written in the shift registers, thus determining the time intervals between the instants of reception of the acoustic emission signals in the respective channels. However, for the apparatus to ensure proper functioning of this data-reading mode, the encoder is inhibited, so that reception of new information is also inhibited. This amounts to a high probability of useful signals of acoustic emission being missed by the apparatus, which significantly impairs the reliability and credibility of the inspection of an article.
Also widely known is an apparatus for determining from acoustic emission signals the coordinates of a crack developing in an article, comprising a plurality of channels each including a series connection of a transducer of acoustic emission signals positionable on an article under inspection and an amplifier of electric signals having its output connected to the respective inputs of a shaper of single pulses and of a unit measuring the parameters of acoustic emission signals. The outputs of the shaper of single pulses and of the unit measuring the parameters of acoustic emission signals are connected to the first and second inputs of the register of the channel. The apparatus further comprises a series connection of a clock pulse generator and a pulse counter having its output connected to the third inputs of the registers of the respective channels. The channels are arranged in groups, the outputs of the registers in each group being united by a common bus serving as a switching device and being connected to the input of a primary data processing unit corresponding to this group. The outputs of the primary data processing units are united by the second common bus and connected to the input of a computer having its output connected to the input of a registration unit.
When a developing crack evolves in the article under inspection, and an acoustic emission signal reaches the channel which is the first to receive this signal, the current time from the commencing of the inspection operation, monitored by the counter, is written into the register of this channel. At the same moment, the register has recorded therein the outcome of the measurement of the parameters of the acoustic emission signal (i.e. its amplitude and duration), and this information is fed to the computer via the switching device. As soon as other channels receive the signal, they also feed their information to the computer. The computer calculates the time intervals between the instants of reception of the acoustic emission signals, computes the coordinates of the source of acoustic emission in the article and assesses its potential hazard.
However, this apparatus would not ensure sufficient reliability and credibility when articles with a high level of inherent activity are inspected. This is explained by the insufficient throughput of the computer which has to handle coded words of an extended size in the appratus being described. To ensure adequate accuracy of computation of time intervals between the instants of reception of acoustic emission signals, the current time should be counted in increments as small as microseconds, and in some cases even as small as fractions of microseconds. However, the maximum value of the current time can be dozens of minutes, hours or even days, depending on the kind of the article under inspection and the test conditions. Thus, the length of coded words representing the current time at the input of the computer can be from 30 to 40 bits, whereas the standard word length of present-day computers is generally from 8 to 16 bits. In other words, the computer of the apparatus being described is doomed to operation (i.e. input, intermediate handling, computation) with words whose length is several times over the standard word length it is rated for. The consequence of the low throughput of the computer can be the loss of acoustic emission information, which, in its turn, affects the reliability and significance of the inspection of an article. Moreover, the apparatus of the prior art being described has an excessive amount of electric connections between its measuring and processing parts, which steps up the noise protection requirements and complicates the designing of the apparatus.